The present invention relates to power units of the kind which on the one hand, propel an associated vehicle, be it on land, sea, or through the air, and on the other hand, provide essential services such as electrical power for lighting, and where the vehicle is an aircraft, a pressurised air atmosphere.
Where the main power unit is a gas turbine propulsion engine, and is installed in an aircraft, it is known to also install an auxiliary gas turbine engine therein, of much smaller proportion than the main engine. The smaller engine is connected with a compressor shaft of the larger engine via an electric motor and on start up of the smaller engine, the electric motor in turn rotates the compressor shaft and thus initiates the starting procedure of the main engine. Furthermore, until such time as the main engine is running, the smaller auxiliary engine also powers other ancillary equipment such as is mentioned hereinbefore. However, when the main engine is running, it takes over from the smaller auxiliary engine, which is then switched off.
The arrangement described hereinbefore has a number of drawbacks, eg the smaller engine also needs an air intake and an exhaust flow outlet, which structures have to be engineered into the aircraft structures, thus creating weight and using space. Furthermore, liquid fuel is used, which either reduces the amount available to the main engine, or necessitates a further supply for the smaller engine, which again adds weight and uses space. Yet a further drawback is created by use of the main engine to drive the ancillary equipment during flight of the associated aircraft, because the power which is diverted from the propulsive effort in order to drive those ancillaries, reduces the efficiency of the engine with regard to its primary task of propelling the associated aircraft through the air.
Gas turbine units are being considered which would be capable of continuous running, so as to enable obviation of use of the propulsion engine to operate the ancillary units. However, they would not obviate most of the drawbacks described hereinbefore.
The present invention seeks to provide an improved dual power system for the propulsion of a vehicle, and the associated ancillary units thereof.
According to the present invention, a vehicle dual power system comprises a gas turbine propulsion engine and ancillary units, an electro chemical fuel cell connected to each via electric motor means, said connection comprising switch means selectively operable such that said electro chemical fuel cell is connected to said electric motor means, to simultaneously cause rotation of a compressor of said gas turbine propulsion engine so as to initiate start up thereof, and to drive said ancillary units, or drive either said compressor or said ancillary units alone.